philosophical_seminarfandomcom-20200213-history
20.01.2010 - Einstein Podolsky Rosen Paradox III
Gaya Ethaniel: Hello Birric :) Birric Forcella: Hi, Gaya Birric Forcella: Gilles was here but then crashed Birric Forcella: Oh, there he is Gaya Ethaniel: ah! Gaya Ethaniel: Hello Gilles :) Gaya Ethaniel: Strange he was online on my friend's list ... Gaya Ethaniel: Even though he crashed as you said. Gilles Kuhn: had problem to log in Gaya Ethaniel: I had problems logging on too. Gilles Kuhn: had heavy problem to connect Gilles Kuhn: sorry Gaya Ethaniel: np :) Gilles Kuhn: and im lagging like hell Gaya Ethaniel: :( Gaya Ethaniel: Gosh, SL is behaving badly ... Gilles Kuhn: well i will try to summon more people Gaya Ethaniel: ok Gilles Kuhn: goddamn that will not be easy tonight Gaya Ethaniel: Shall I try? Gilles Kuhn: yes please i have no access to my groups..... Bau Ur: Hi! Bau Ur: Is a discussion going on? Gilles Kuhn: well we seems to be subjected to a quantum vicious singularity..... Cosmo Fenwitch: I hate it when that happens. Gilles Kuhn: it would normally be if sl would behave a bit Gilles Kuhn: me too cosmo Gilles Kuhn: hello bau Bau Ur: :) Bau Ur: Is this normally a science discussion area? I was here once for a lecture. Gilles Kuhn: well i have no access to groups when i write something it appear 50 percent on time and with a big delay Gilles Kuhn: so welcome to the philosophical seminar sl wanting we will continue our debate on the epr paradox Bau Ur: alas I do not know what the epr paradox is. Is there a reading online? Gilles Kuhn: yes consult philosophical seminar group info bau Bau Ur: I was running through my landmark collection, that's why I arrived here just now. Is a formal discussion about to begin? Gilles Kuhn: so last time three week ago and my apologies for the two weeks gap Gilles Kuhn: we have saw the first part of podolsky argument Birric Forcella: I'm back Gilles Kuhn: wb birric Gilles Kuhn: hope you dont experience the horrific tech problem i have Gaya Ethaniel: wb :) Gilles Kuhn: so the plan tonight was to expose and discuss the second part Birric Forcella: I changed computer. I hope it helps Gilles Kuhn: in the first part under the premise that a theory must be complete and the reality is defined by the capacity of measurement of a physical quantity Bau Ur: http://www.drchinese.com/David/EPR.pdf Gilles Kuhn: podolsky showed basing itself on qm equations that or 1 qm is not a complete desscription of physical reality or 2 two if the operator corresponding to different physical variable dont commute then only one of them has a physical reality and the other has not Gilles Kuhn: that was where we have got last time so before starting the second part of the paper question? Gilles Kuhn: ok then let see the second part of podolsky argument Gaya Ethaniel: ok Gilles Kuhn: let take not one but two system that interact during a certain time Birric Forcella: Let me restate Podolsky's postulate. It basically says that there cannot be any jumps in nature, but that everything must be smoothly grained and "all the way down." Gilles Kuhn: well that s a manner to put it Birric Forcella: The "all the way down" is crucial. Basically there cannot be a bar to the fineness of measurement Gilles Kuhn: well it can be one but then there is no physical reality to it Birric Forcella: Well, that's the same as saying that it applies to ALL physical REALITY Gilles Kuhn: and so in the first part if you have a measure of a physical quantity that is not commuting to another then the another is not existing as a physical reality due to podolsky postulates and premises Gilles Kuhn: yes but that s already a generalisation of the argument Gilles Kuhn: so let focus first on the second part Gilles Kuhn: let have two system interacting during a certain time but not more HABLE to do so after Gilles Kuhn: if we know the state of the two system before they cease to interact we can assign to both of them a wave function according to schrodinger equation Gilles Kuhn: this wave function will describe their state after their interaction cease Gilles Kuhn: but we cannot determine the precise state of any of the two system without doing a measurement and that will " collapse " the wave Gaya Ethaniel: hm ... I thought the wave function would describe simultaneous reality of the two state not afterwards ... did I get that wrong? Gaya Ethaniel: two states while interacting Gilles Kuhn: to resume the quite formal argument of podolsky if you do so i e if you measure one of the system then you collapse his wave packet Gilles Kuhn: well the wave function of the two system will describe both of them after the interaction Gilles Kuhn: the wave function big psy is the wave function describing the evolution of both the system even if they cannot more interact Gaya Ethaniel: ah ... I see what you mean Gilles. Simple misunderstanding ... ^^;;; the wave function is a snapshot of the interaction of course. Gilles Kuhn: the problem is if that you make a measure of ONE of the systems then you collapse this unique wave packet !!!! Gilles Kuhn: so measuring one system that no longer interact with the other will determine the other as well Gilles Kuhn: and there is the core of the paradox Birric Forcella: Maybe you should first say something about the interpretation of the wave function Gilles Kuhn: please do so birric Birric Forcella: Well, the wave, for one or more systems, was first interpreted as the ACTUAL particle/matter thingy. Gilles Kuhn: yes that was before Copenhagen interpretation Birric Forcella: You may remember that the slit and two slip experiments showed that matter was a wave Birric Forcella: So the first thought was that matter actually IS a wave and that the wave is somehow MATERIAL Gilles Kuhn: well i would say acted as to be modelled by a wave function Birric Forcella: However, soon it was found that that was untenable Birric Forcella: Then the interpretation was that the wave basically defined the probability of finding the ACTUAL matter thingy. Gilles Kuhn: by actual matter thingy we mean physical quantities like position speed spin charge etc Birric Forcella: However, it soon turned out that that was also untenable and that it was almost impossible to say WHAT that wave is. Birric Forcella: And that means, we also cannot say what MATTER is Gaya Ethaniel was wondering about 'thingy' thanks Gilles :) Birric Forcella: Some interpretations actually say that matter IS merely the probability of finding it Birric Forcella: And that matter ONLY pops into existence when it is really actually found Gilles Kuhn: yes but that is before instrumentalism when we define as podolsky physical reality by capacity of measurement and determination of quantities as the criterium of reality of "what" Gaya Ethaniel: What is the difference between 'found' as Birric says and 'measured' as in observed? Birric Forcella: That is the "wave collapse" - When you look at the thing, the probability of finding a piece of matter actually changes into an actuality of having FOUND it. Gilles Kuhn: none Birric Forcella: You may remember claims like that "the moon is not really there unless somebody looks at it." Gilles Kuhn: not found it measured a quantity that show on our instrument Gilles Kuhn: well it is perhaps there but you cannot assign to its presence a 100% probability Birric Forcella: As it turns out, matter waves can be HUGE. A photon coming from a very far galaxy can have a wave (due to spreading) as big as the solar system Birric Forcella: Nevertheless, the second it gets detected in an astronomer's telescope and looked at - it apparently "collapses." Gilles Kuhn: this 100%, probability is only accessible by measurement but a measure collapse the wave function and so destroy the capacity to observe all the others physical quantities but that one you choose to determine Birric Forcella: Right Gaya Ethaniel: "100% probability" - you mean it may not exist or it could but what is being seen may Or what is being observed may not match what it really is? Birric Forcella: There is a lot more weirdness associated. But I think Gilles wants to now concentrate on the fact that when waves interact, they superimpose and can each carry part of the other away for far distances. Gaya Ethaniel: hm ... maybe those two cases are same ... Gilles Kuhn: well to take moon example you can say it is still there when you see it (well at two second delay) but if you don't see it you can only a sign a probability however huge one Gilles Kuhn: indeed birric Gaya Ethaniel: ok Gilles Kuhn: podolsky show that you create two wave function different one but in the same reality which is paradoxical Gilles Kuhn: in more technical word the thought experiment show that you can have two physical quantities not commuting but having both simultaneous reality in the sense defined in the first part of the paper Gilles Kuhn: in a more experimental manner you can show and it was show experimentally by Aspect that if you measure one of the system the other will " react to the measurement of the first as if it was aware of the measure and the wave function collapse even when it could not interact anymore with the first !!! Gaya Ethaniel: I know it is very cool :) Gilles Kuhn: which mean that the wave function collapse seems to be immediate and so don't respect at all einstein special relativity Gilles Kuhn: other have spoke of non locality to "explain " that Birric Forcella: Let me get back to the simple underlying philosophy here. EPR are trying to establish a "reductio ad absurdum" argument. They are saying: "Look, Mr. Bohr, these are the implications of QM - but it's simply impossible because they lead to contradictions." Gilles Kuhn: indeedd birric but problem as always with qm the theory was confirmed ALWAYS by the experiments Gaya Ethaniel: Generally though contradiction means having a fixed position to be compared with. Gilles Kuhn: and so if i was popperian i would say that einstein special relativity seems to be falsified Birric Forcella: Right, that is exactly the point. EPR make the EPISTEMOLOGICAL claim that it is impossible - And Bohr answers that ONTOLOGICALLY it happens anyway Cosmo Fenwitch: It does seem spooky, like magic, but there is no contradiction and it is possible since it happens. Gilles Kuhn: or you have to introduce hidden variable Gilles Kuhn: well and aspect show that EMPIRICALLY it happens too ! Birric Forcella: Let me try to bring out more clearly WHAT the paradox is. Birric Forcella: You can make an atom emit two particles at the same time in different directions. The particles have related but opposite properties, like spin, or, lets say if one is green, then the other is always blue Birric Forcella: Now the classical view would say that the particles are green and blue from the moment of the emission Birric Forcella: However, remember, QM says that the color does not get "real" until the particles are measured Birric Forcella: So EPR objection is this: If the two particles fly for a long time, and are, let's say, light years apart, and THEN you make the measurement - it would mean that if the ONE does not get its color until the measurement, then the OTHER does not either Gilles Kuhn: well podolsky interpretation of qm say that but i will not discuss the word real at the moment Birric Forcella: Which means, they would have to be at INSTANT communication over light years Birric Forcella: Since, the other has to have the complementary color Gilles Kuhn: and aspect showed indeed that is what happen ....empirically TR Amat: If I understand the research, the connection seems to be instant, but, no information is transferred at faster than light speed. Gaya Ethaniel: Thought quantum entanglement is accepted Birric? Gilles Kuhn: well not exactly you cannot use the trick to transmit new info thats all Birric Forcella: Now remember, that INSTANT communication does not only destroy Relativity, it also philosophically destroys some very basic assumptions about reality - like it would allow "magic." Gilles Kuhn: well in that i disagree birric Gilles Kuhn: desccartes and spinoza physic were based on instant communication Gilles Kuhn: so you can logically devise physical system who permit them TR Amat: I understand there was some proposal to use quantum entanglement to give you one time pads, that you could then use for secure communication over conventional connections? Gilles Kuhn: but we have a problem that in our actual theoretical state of affair relativity is very very efficient Birric Forcella: TR, apparently the effect cannot be used by US to transfer information faster than light - however, there must be some info communicated - because the particle 'knows" what color it is supposed to have immediately Cosmo Fenwitch: But ther is no instant "communication" since no information is transferred. Gaya Ethaniel: Simultaneous or instant? Gilles Kuhn: in our perspective of information transferring no cosmo indeed Cosmo Fenwitch: Event the concept of instant is not well defined over long distances since simultaneous is relative to speed. Gaya Ethaniel: Yes both words seems to imply distance, speed etc ... Cosmo Fenwitch: For different observers either measurement could have been made first. Gilles Kuhn: and the rub is that indeed is any info transferred in fact the question reduce to the problem of the collapse of the wave the paradox is show more evidently with two system entangled but basically it is the same problem with a single system Gilles Kuhn: aspect experiment adress that in a very precise manner cosmo TR Amat: I believe one way of looking at it is light cones, and, current research doesn't show a way of getting the effect to occur before the cause. Gilles Kuhn: as in aspect experiment the measure are made simultaneously and recorded independently and then checked after : epr always work Gilles Kuhn: before no but simultaneously seems that yes... Cosmo Fenwitch: What does simultaneous mean? For other experimenters in a different frame of motion, they would not have been simultaneous. Birric Forcella: You have to realize that the EPR thought experiment and Bell's inequality are only used to make the paradox very obvious. The problem exists with ALL matter. Remember when I said that a photon may be spread out over the size of the solar system. Nevertheless, when that wave collapses, clearly ALL parts of the wave must know instantly about it. Now, this is the case for ALL matter, even the atoms in your body. They are not that far spread apart, but they still are "smeared" quantum particles - and every collapse of them would involve the same effect - an instantaneous collapse and communication over space. Gilles Kuhn: simultaneous as measured by two different very precise clock Gilles Kuhn: perfectly put birric ! TR Amat: Tends to suggest shortcomings in our understanding of what time is? Gilles Kuhn: of what space time is Gilles Kuhn: i am sorry but i cannot stay more online we shall resume next week if sl permit..... Stim Morane: Thanks, Gilles and everyone Gaya Ethaniel: Thanks Gilles :) Gilles Kuhn: (need to feed and let go out two rl canine ....) Birric Forcella: At some point we should get back to the meaning of all this for Free Will. That's what started all this off Gaya Ethaniel: Enjoy your day! Gilles Kuhn: agreed birric Birric Forcella: Thanks, Gilles Gaya Ethaniel: Yes :) Gilles Kuhn: thanks to you all and sorry for the last two weeks murphy laws fully applied ....